Production of foamed sand using near infrared

ABSTRACT

An arrangement for producing a bulk material consisting substantially of foamed or blown mineral or oxide particles by thermal treatment of a bulk material of basic particles. The arrangement includes NIR halogen radiators for generating a NIR radiation field of radiation with an active component in a near infrared, NIR, range having a wavelength in a range between 0.8 μm and 1.5 μm and which has a power density of at least 50 kW/m 2  for thermally treating the basic particles, a conveying device for transporting a layer or stream of the bed of basic particles through the radiation field, and a controller that controls heating of the bed of basic particles such that a maximum temperature in the layer or stream is in a temperature range between 600 and 1500° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/641,319, filed Feb. 24, 2020, which is a 371 National Phase ofPCT/DE2018/100731, filed Aug. 24, 2018, which claims priority fromGerman Patent Application No. 10 2017 119 371.5, filed Aug. 24, 2017,all of which are incorporated herein by reference as if fully set forth.

TECHNICAL FIELD

The invention relates to a method for producing a bulk materialessentially from foamed or blown mineral or oxidic particles by thermaltreatment of a bulk material of basic particles and an arrangement forcarrying out this process.

BACKGROUND

In the context of global efforts to protect the climate, there is acontinuously high and increasing demand for cost-effective insulatingmaterials with a wide range of applications. In view of the fact thatcertain insulation materials used on a large scale (e.g.polystyrene-based) have to be substituted in certain areas ofapplication due to problems with fire protection and environmentallysound disposal, there is a particular need for substitute materials thatcan be widely used in the construction industry.

In recent years, there have therefore been developments to extract abulk material from certain sands by thermal treatment from particleswith air inclusions and, as a result, very good thermal insulationproperties, which is sometimes referred to as “expanded sand”. Inaddition to their extremely low thermal conductivity, these expandedsands have a high temperature resistance and low heat capacity and canbe processed with known binders to produce a variety of products thatcan be widely used in the construction industry, such as insulatingplasters, insulating fillers for construction elements (e.g. bricks),fire protection cladding, quick-drying screeds, etc.

Such expanded sands are now commercially available. They are producedwith “open flame”, which leads, among other things, to an unsatisfactoryyield of usable end product and relatively high costs for the separationof unusable parts of the immediate process product.

SUMMARY

The invention is therefore based on the object of specifying an improvedmethod for the production of such bulk materials and an arrangementsuitable for carrying out this process.

This object is met in its method aspect by a method with one or morefeatures described herein and in its device aspect by an arrangementwith one or more features as described herein. Appropriate furtherdevelopments of the inventive idea are described below and in theclaims.

The invention includes the idea of exposing the starting product, i.e. abulk of mineral or oxidic basic particles, to a thermal treatment withshort-wave infrared radiation, especially radiation in the near infraredrange (with a wavelength of about 0.8 to 1.5 μm) in order to achieve thedesired swelling or foaming of the basic particles. Furthermore, theinvention includes the idea of allowing the said short-wave infraredradiation (NIR radiation) to act on a layer transported through aradiation field or a trickle stream of the basic particles, i.e. toprovide for continuous process control. In addition, the inventionincludes the idea of using a NIR radiation field with high power densityin the interest of high efficiency of expansion/foaming and highthroughput. This should typically be at least above 50 kW/m², preferablyeven much higher.

In a practically relevant embodiment of the method, the basic particlesare a sand with a high water glass content, especially with a grain sizein the range of 50-500 μm and a water glass content of at least 40%.

Such sands are a widely available and very cost-effective startingproduct, and their processing is unproblematic from an environmental andoccupational safety point of view.

As a result of the method, a bulk material is then preferably obtainedfrom foamed or blown sand particles, which at the end of the thermaltreatment, without a separation step, comprises a proportion of 60%, inparticular 80%, perlite particles with an essentially closed surfaceand/or in which the particle size is in the range of 0.3 mm-2 mm. Such amethod product is particularly well suited for use in various productswith high insulating properties and is also particularly cost-effectivebecause a large proportion of the starting product is converted into ausable end product.

In a preferred embodiment, an infrared radiator array with a radiationtemperature of 2900 K or more, preferably 3200 K or more, is used forthe proposed drying process. According to the inventors' findings, itsradiation spectrum is particularly suitable for the thermal dewateringof bulk material, especially of powdery or flittery consistency.

The use of an arrangement with several halogen lamps with correspondingradiator temperature is also preferred, whose radiation is concentratedor focused on the passing flow of the source material to be treated byassigned reflection surfaces. In a preferred embodiment, additionalreflectors or reflection surfaces are provided on the side of theproduct stream facing away from the radiation source(s). Thesereflectors or reflection surfaces deflect a part of the NIR radiationnot absorbed by the product stream during the first pass back into theproduct stream. This further increases the radiation yield and thus theenergy efficiency of the treatment process.

Even more preferred is such a design of the plant that the irradiationarea forms a largely closed radiation chamber, which is only open to theextent required for the transport of the product stream.

Depending on the specific chemical composition and the moisture contentof the bulk material, a period of time in the range between 0.5 and 20s, in particular between 1 and 5 s, is provided for treatment with NIRradiation. The duration of time is adjusted by the length of the NIRradiation field and the transport speed of the conveyor system when thestarting material is conveyed horizontally or at an angle. If the NIRirradiation takes place in a trickle stream, the dwell time in theradiation field can be adjusted appropriately by the air velocity of anair stream directed against the trickle stream.

In the core area of thermal treatment, the maximum temperature of thebulk material is preferably set in the range between 600 and 1500° C.,especially 800 to 1200° C.

The power density of the NIR radiation is preferably adjusted to valuesabove 300 kW/m², especially to more than 500 kW/m², in order to achievea short treatment duration.

Its layer thickness of the starting material in the radiation field ispreferably set to a value between 2 mm and 30 mm, even more specificallybetween 5 mm and 20 mm.

In another embodiment, the bulk material is transported through an NIRradiation field with several heating areas with different powerdensities. This allows, if necessary in view of the properties of thestarting product and the desired properties of the end product, targetedpreheating and/or temperature equalization in addition to a main heatingstep. This is also possible in a further embodiment in which at leastone further thermal treatment step is carried out in addition to thetransport through the radiation field with NIR radiation.

The latter embodiment may be specially designed so that the layer of thebed of basic particles, in particular on a vibrating table or inclinedconveyor, is transported horizontally or at an angle through theradiation field with near infrared radiation and is thereby thermallypre-treated and the thermally pre-treated bed is then subjected topost-treatment in an induction furnace or a second radiation field withinfrared radiation. The infrared radiation of the second radiation fielddoes not necessarily have to be NIR radiation, but a conventionalindustrial furnace with long-wave IR radiation or resistance heating canalso be used.

In a further embodiment, the subsequent treatment step is carried out ina, in particular vertical, multi-zone furnace, whose heating zones haveincreasing temperatures from the inlet to the outlet. Even morespecifically, the temperature of the first heating zone can be set inthe range between 950 and 1050° C., the temperature in a second heatingzone in the range between 1050° C. and 1150° C. and the temperature in athird heating zone in the range between 1150° C. and 1250° C.

In a further embodiment, after the thermal treatment, a rapid cooling ofthe bulk material is carried out, in particular by letting it impinge onan actively cooled cooling surface.

In a practically relevant embodiment, the method further comprises aseparation step of separating the foamed or blown particles fromnon-foamed or non-blown basic particles on the basis of their differentspecific weight, in particular in a cyclone separator or in a rising airstream. It appears to be particularly efficient if the separation stepis carried out together with the thermal treatment or a thermaltreatment step or a cooling step in one and the same part of the plant,especially in the rising air flow in a vertical furnace or cooler.

Device aspects of the present invention arise for the person skilled inthe art largely from the method aspects explained above, so that in thisrespect repetitions are avoided. However, reference is made to someembodiments of the proposed arrangement.

In one embodiment, the NIR radiation field has several heating areaswith separate control, especially for setting different power densities.Alternatively or additionally, the arrangement may include a multi-zonefurnace with an inductive or infrared heating system, which is arrangeddownstream of the NIR radiation field, especially in the transportdirection of the bulk material, and/or in particular is orientedvertically.

In a further embodiment, the transport device has a vibrating table,belt conveyor or drum conveyor, wherein in the case of a drum conveyor,the flat arrangement of NIR halogen emitters is curved to match aperipheral surface of the drum conveyor.

In a further embodiment, the arrangement includes a cooling device forrapid cooling of the thermally treated bulk material, which inparticular comprises an actively cooled cooling surface on which thebulk material impinges.

Another embodiment has a separating device for separating the foamed orblown particles from non-foamed or non-blown basic particles due totheir different specific weight, in particular a cyclone separator or afan for generating a rising air flow.

In the interest of a simultaneously cost-effective and compact design ofthe plant, an embodiment is of interest in which the vertical multi-zonefurnace and the fan for generating an ascending air flow arestructurally combined in such a way that the separation step is carriedout in conjunction with a thermal treatment step in the multi-zonefurnace or a cooling step.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and usefulness of the invention are further described inthe following embodiment example by reference to the FIGURE.

The sole FIGURE is a diagrammatic representation of a production linefor the production of foamed sand.

DETAILED DESCRIPTION

The FIGURE shows a synoptic representation of a production line 1 forthe production of foamed sand as a thermally treated bulk material 3made of normal sand 3′ containing water glass as starting material.

A screw conveyor 5 conveys the sand 3′ into an NIR treatment station 7,in which an NIR emitter module 7 a is arranged above an oscillatingconveyor 7 b and NIR irradiation of the starting material continuouslyconveyed through the irradiation station 7 is carried out withpredetermined power density and dwell time. The setting of the powerdensity and the dwell time (via the conveying speed of the oscillatingconveyor 7 b) is controlled by a process control unit or controller 9After leaving the NIR treatment station 7, the pre-treated materialenters a vertical furnace 11 with inductive heating, which comprisesthree heating zones 11 a, 11 b, 11 c with independently adjustabletemperature and in which the thermal treatment of the sand is completed.Also the treatment in vertical furnace 11 and especially thetemperatures in the heating zones 11 a-11 c are controlled by theprocess control unit 9.

The thermally blown or foamed sand is cooled in a cooling system 13,which includes (not shown) cooling air fans and a cooling pipe 13 a. Itis then fed to a cyclone separator 15, where the non-blown productfraction 3′ is separated from the final product 3 with the desiredproperties. While the thermally unmodified starting product 3′ enters astorage container 17 from where it can be brought back to the startingpoint of the process, the cleaned end product is blown into a fabric bag19.

The execution of the invention is not limited to this example, but isalso possible in a variety of modifications, which are within the scopeof professional action.

1. An arrangement for producing a bulk material essentially from foamedor blown mineral or oxidic particles by thermal treatment of a bed ofbasic particles, the arrangement comprising: a flat arrangement of NIRhalogen radiators for generating a NIR radiation field of radiationwhose essential active component is in a near infrared, NIR, rangehaving a wavelength in a range between 0.8 μm and 1.5 μm and which has apower density of at least 50 kW/m² for thermally treating the basicparticles; a conveying device for transporting a layer or stream of thebed of basic particles through the radiation field; and a controllerthat controls heating of the bed of basic particles such that a maximumtemperature in the layer or in the stream is in a temperature rangebetween 600 and 1500° C.
 2. The arrangement according to claim 1,wherein the NIR radiation field comprises several heating areas withseparate controls for setting different power densities.
 3. Thearrangement according to claim 1, wherein the transport device comprisesa vibrating table, belt conveyor or drum conveyor, wherein for the drumconveyor the flat arrangement of NIR halogen emitters is curved to matcha peripheral surface of the drum conveyor.
 4. The arrangement accordingto claim 1, further comprising a multi-zone furnace with an inductive orinfrared heating system, which is at least one of arranged in atransport direction of the bed downstream of the NIR radiation field oris oriented vertically.
 5. The arrangement according to claim 4, furthercomprising a cooling device for rapid cooling of the thermally treatedbulk material, which comprises an actively cooled cooling surface onwhich the bulk material impinges.
 6. The arrangement according to claim5, further comprising a separating device for separating the foamed orblown particles from non-foamed or non-blown basic particles based on adifferent specific weight of the particles, the separating devicecomprising a cyclone separator or a fan for generating a rising airstream.
 7. The arrangement according to claim 6, wherein the multi-zonefurnace is arranged vertically, and the fan for generating an ascendingair flow is structurally combined with the multi-zone furnace such thatthe separation step is carried out in conjunction with the thermaltreatment step in the multi-zone furnace or a cooling step.